In TDD (Time Division Duplex) radio communication systems, there are ones that use an eigenvector(s) obtained by eigenvalue decomposition as a beam forming weight(s) in transmission/reception of a signal in order to improve the radio characteristics. Patent literatures 1 and 2 disclose a technique in which eigenvalue decomposition is performed on a reception signal of an uplink (communication line from a terminal station to a base station) and a transmission beam of a downlink (communication line from the base station to the terminal station) is formed by using its result.
Further, Non-patent literature 1 introduces a beam forming method in which attention is paid to the correlation-present property and the correlation-absent property of antennas. This literature shows an example of Grouped EBB (Eigenvalue-Based Beamforming: beam forming based on eigenvalue decomposition) under an assumption that, for provided antenna, a plurality of polarized antennas are arranged in a linear array.